Investigations of Carbon Sequestration Mechanisms in Partially Depleted Oil Reservoirs

The objective of this work is to evaluate various CO₂ trapping mechanisms and long-term carbon storage potential involved in CO₂ enhanced oil recovery (EOR) projects in a partial depleted sandstone oil reservoir. More importantly, we seek to confirm changes in petrophysical properties induced by CO₂ injection that have been observed from laboratory measurement. A field-scale numerical simulation model is established utilizing extensive field data to study the Upper Pennsylvanian Morrow B sandstone. The validity of the reservoir model is confirmed via a rigorous history matching study using field injection and production data. The history-matched model is employed to assess the multiple trapping mechanisms including residual trapping, structural-stratigraphic trapping, solubility trapping and mineral trapping. Numerical experiments are conducted considering the intra-aqueous and mineral dissolution/precipitation reactions, which may promote pore structure alterations. Moreover, we take advantage of Henry’s law to calculate the CO₂ dissolution as function of pressure, temperature and salinity. The reservoir is monitored for 1000 years after all the injectors and producers are shut-in to investigate the long-term storage of CO₂ injection in the field. Such a robust reservoir model is compentent to evaluate long-term CO₂ sequestration potential and study the impact of the CO₂ injection on petrophysical properties of the Morrow-B formation, such as pore fluid composition, mineralogy, porosity and permeability. The results from this work provide significant insights in terms of the optimum storage of CO₂ in aqueous-gaseous-mineral phases, effect of salinity on storage, and the amounts of dissolution/precipitation of the principal accessory minerals evolving throughout the project. Information gained from this study offers valuable insight regarding physiochemical storage induced by the CO₂ injection activities and may serve as a benchmark case for future CO₂ -EOR projects when reactive transportations are considered.